Background/Question/Methods
Host-microbe symbioses play a critical role in the evolution of biological diversity and complexity. Potential problems with such associations arise because of the host’s reliance on its microbial symbiont. Any impact to the fitness of the mutualist will also have negative cost to the host. In a well-known example of this, fungus-growing ants obligately depend on fungi for food and the success of fungal cultivation is threatened by specialized microfungal parasites. To help protect their food supply, fungus-growing ant’s engage in mutualism with antibiotic-producing actinomycetous bacteria. We decided to test whether this relationship was unique to fungus growing ants or was more prevalent in nature. In a notably intricate system, southern pine beetles use symbiotic fungi to help overcome host-tree defences and to provide nutrition for their larvae. Here we show that an actinomycete-produced polyunsaturated peroxide chemically mediates the southern pine beetle-fungal mutualism.
Results/Conclusions
The molecule’s selective toxicity towards the beetle's fungal antagonist, combined with the prevalence and localization of its bacterial source, indicates an insect-microbe association that is both mutualistic and coevolved. This unexpected discovery in a well-studied system indicates that mutualistic associations between insects and antibiotic-producing bacteria are more common than currently recognized, and that these associations may be crucial to the success of the host, both evolutionarily and ecologically.